1. Field of the Invention
The present invention is directed to a method and an arrangement for reducing printer errors during printing in a mail-processing device. The invention is utilized in postage meter machines, addressing machines and other printing mail processing devices.
2. Description of the Prior Art
In the field of digital printing, the variable part of the print image is becoming more extensive and the print resolution is becoming higher. For example, the variable print image part should be flexible for different postal demands and should be modified from imprint to imprint. At the same time, the controller is burdened with other extensive tasks. For relieving the microprocessor control, it has proven advantageous to arrange the pixel data belonging to a print image column in the pixel memory such that variable picture elements can be modified by the microprocessor in the available time. It has also proven advantageous to relieve the microprocessor responsible for the control of the printing mail processing device or system by using a print data controller for the control of the printing. The printing requires a relative movement between a printhead and a print medium, for example a sheet-like article, letter, postcard, package, franking tape, address sticker or label.
U.S. Pat. No. 6,467,901 and German OS 100 32 855 disclose a device for printing on a print medium that is utilized in a mail processing device such as in the postage meter machine ultimail® of Francotyp Postalia AG & Co. KG. The print media, for example letter envelopes, franking tapes or comparable franking material, are transported downstream in the mail stream in a transport direction by a driven transport drum, with a non-driven counter-pressure device pressing the print medium against the transport drum in a direction orthogonal to the transport direction. The two ink cartridges project partially into the transport drum and carry two ink jet printheads that undertake the printing on the moving print medium in non-contacting fashion. Both printheads are arranged orthogonal to the transport direction and orthogonal to the counter-pressure direction with their nozzles close to the edge of the transport drum, whereby the nozzles can generate a complete imprint in one pass of the print medium through the machine. Markings that are distributed around the circumference of the transport drum are applied to the end face of the transport drum close to the circumference. For example, the markings are reflective lines that are detected by a reflection barrier or transmitted light barrier of an encoder and are converted into printing pulses in the ratio 1:1 by the microprocessor of a controller. Gradual, slow fluctuations in the transport speed thus have no influence on a generated print image when the duration of the print cycle is modified.
According to the manufacturer of the printhead, a print cycle should optimally amount to 90% of the time between two positive encoder edges. The time between the encoder edges can be measured, and the duration of the print cycle can be correspondingly set. After being determined, however, the set value for the print cycle duration takes effect with a delay of at least two encoder clocks. Sudden variation in the transport speed can be caused by changes in the letter thickness and mechanical oscillations of the encoder sampling system. The sudden fluctuations in the transport speed, however, have a negative influence on a generated print image, printer errors due to spacings between the encoder pulses that are too small must be expected despite a subsequent adaptation of the print cycle duration to the distances between the encoder edges.